I had the priviledge, a number of years ago, to learn a number of things from a Marine Colonel who worked in the Marine Marksmanship Unit Armorers shop, back in the "late Garand, Early M14" era. One of the things he schooled me on was those neat little chamber adapters that let you shoot .308 in a .30-06 Garand.
The proper proceedure of installation involved reaming some radial grooves into the '06 chamber, seating the insert in the chamber, then firing a lubed proof round in it to expand the insert to permanently in the grooves - so it wasn't going anywhere, ever.
However, the inserts sold by Sarco and other companies (at least in the early 90's) were NOT of completely correct dimensions, and he called them "of suspect parantage".
The idea of having the stupid thing fly out wrapped around a .308 brass, and following it up with another round makes me uncomfortable.
Seems the Navy abandoned the inserts, after figuring out it wasn't that big a labor savings over just rebarreling it in .308, and having trouble with them not getting permanently enough seated.
I've seen only one rifle with what appeared to be a Navy installed insert in it. I've also seen one pulled barrel that had what looked like the grooves for an insert cut in it.. But no insert. I'm sure there are more out there.. But Those are the only o es I've seen.
To the original question; buy a new barrel, or a new rifle. You can't have too many (just not enough safe space).